1. Field of the Invention
The present invention relates to a Heusler alloy having a magneto-optical effect and particularly to a material suitable for writing magnetically and reading out optically, and to a process for preparing the same.
2. Description of the Prior Art
A Heusler alloy having a magneto-optical effect is described in Applied Physics Letters, 42 (2) (1983), pp. 202 to 204. According to this article, in the case of, for example, PtMnSb, raw materials are heated in a Mo crucible at 850.degree. C. under a reduced Ar pressure for a long time (two weeks) to obtain a polycrystal sample. The flat portion of the sample is subjected to mirror polishing. A high magnetic field of 1.2 T is vertically applied to the polished surface to obtain a high Kerr rotation of 0.93.degree. at a wavelength of 633 nm.
On the other hand, attempts to form a thin film have been made in consideration to application thereof as a device. As described in Nippon Oyo Jiki Gakkaishi, Vol. 9, No. 2 (1985), P. 145, a polycrystalline thin film of an alloy having a composition of Pt.sub.x (MnSb).sub.1-x (where x=0 to 0.2) is prepared by an r.f. sputter method, and heat-treated at 500.degree. C. under a vacuum of 1.times.10.sup.-5 Torr for 10 hours. A Kerr rotation of 0.9.degree. is obtained at a wavelength of 633 nm in a perpendicular magnetic field of 4.0 kOe. The coercivity Hc in the in-plane direction is 110 Oe.
The magnetic thin film obtained by the above-mentioned conventional technique is relatively easier to magnetize in the in-plane direction than in the vertical direction. It is desired from the viewpoint of application thereof as a device that it is further easier to magnetize. Particularly, the Hc is preferably as low as possible when consideration is given to application of a magnetic thin film as a device such as a head for writing magnetically and reading out optically.